In The Name of Allah The Most Beneficent The Most Merciful

M.R.I Magnetic Resonance

Imaging

Group Members:

EE-01083-062 M Aqil YousafEE-01083-166 M Talha

IntroductionIn this presentation the topic under

discussion will be

MRI introduction

Nuclear Spin Properties

Block Diagram

Applications

Limitations

MRI Magnetic resonance imaging (MRI) is a

test that uses a magnetic field and pulses of radio wave energy to make pictures of organs and structures inside the body

MRI introduction

Intensity wise differentiation Fat high (whitish) Muscle intermediate

(gray) Ligaments & Tendons low (dark gray) Immature Scar intermediate -

low

History Background

In the 1950s, Herman Carr reported on the creation of a one-dimensional MRI image. Paul Lauterbur expanded on Carr's technique and developed a way to generate the first MRI images, in 2D and 3D, using gradients. In 1973, Lauterbur published the first nuclear magnetic resonance image. and the first cross-sectional image of a living mouse was published in January 1974

MRI introduction

ProcedureMagnetic nuclei are abundant in the human body (H,C,Na,P,K) and spin randomly

Since most of the body is H2O, the Hydrogen nucleus is especially prevalent

• Patient is placed in a static magnetic field• Magnetized protons (spinning H nuclei) in the patient align in this

field like compass needles• Radio frequency (RF) pulses then bombard the magnetized nuclei

causing them to flip around• The nuclei absorb the RF energy and enter an excited state

• When the magnet is turned off, excited nuclei return to normal state & give off RF energy• The energy given off reflect the number of protons in a “slice”

of tissue• Different tissues absorb & give off different amounts of RF energy

(different resonances)• The RF energy given off is picked up by the receiver coil &

transformed into images

MRI introduction

What kinds of nuclei can be used for ?

Nucleus needs to have 2 properties: Spin charge

Nuclei are made of protons and neutrons Both have spin ½ Protons have charge

Pairs of spins tend to cancel, so only atoms with an odd number of protons or neutrons have spin Good MR nuclei are 1H, 13C, 19F, 23Na, 31P

MRI introduction

Hydrogen atoms are best for MRI

Biological tissues are predominantly 12C, 16O, 1H, and 14N

Hydrogen atom is the only major species that is MR sensitive

Hydrogen is the most abundant atom in the body

The majority of hydrogen is in water (H2O) Essentially all MRI is hydrogen (proton)

imaging

Nuclear Spin Properties

A Single Proton

++

+

There is electric charge on the surface of the proton, thus creating a small current loop and generating magnetic moment m.

The proton also has mass which generates anangular momentumJ when it is spinning.

Jm

Thus proton “magnet” differs from the magnetic bar in that italso possesses angular momentum caused by spinning.

Nuclear Spin Properties

How do protons interact with a magnetic field ?

Moving (spinning) charged particle generates its own little magnetic field Such particles will tend to line up with

external magnetic field lines (think of iron filings around a magnet)

Spinning particles with mass have angular momentum Angular momentum resists attempts to

change the spin orientation (think of a gyroscope)

Nuclear Spin Properties

Machine Working

Application Clinical neurology– Segmentation and classification– Measuring volumes of brain structures– Multiple sclerosis, stroke, … Cardiology– Either need to image fast, or deal with heart motion! Cancer–colorectal, liver, prostate, … Soft tissue damage – Cartilage, ligaments, …

Limitations of MRI

Some patients experience claustrophobia and have difficulty in cooperating with the study. 

Some obese patients cannot be examined. Some patients, particularly acutely ill patients, cannot cooperate

and movement artifacts may result.  Patient throughput is slow compared with other imaging

modalities.  Patients with pacemakers and certain ferromagnetic

appliances cannot be studied. Greater technological expertise is required for performance

of MRI than for most other imaging modalities.  MRI equipment is expensive to purchase, maintain, and

operate.

Questions

Please !!!